1. Field of the Invention
This invention resides in the field of thrust nozzles for liquid-fuel rocket engines, and addresses in particular the means by which the nozzle is cooled.
2. Description of the Prior Art
The high pressure at which liquid-propellant rocket engines operate and the high temperature attendant to the high pressure make efficient and effective cooling of the thrust nozzle a necessity. One cooling method currently in use is the incorporation of coolant channels in the walls of the nozzle by forming the nozzle walls from platelet laminates with engineered channels formed by openings etched through the platelets. With supersonic nozzle geometries, however, The construction of nozzles with this type of channel is a complex process for supersonic nozzles, however, in view of the compound curvature that is typical of supersonic nozzles. The nozzle is generally formed in two or more lengthwise sections that are welded together along axially oriented seams. The seams are areas of potential material failure and discontinuity, particularly in the coolant channels. Further risks arise from the arrangement of the individual coolant channels, particularly those whose width is on the order of 0.05 cm. When localized hot gas (i.e., a portion of the gas that is at a higher temperature than the surrounding gas) occurs in the combustion chamber, a hot streak can form along the inner wall of the chamber as the gas flows axially through the chamber, and the streak can cause excessive heating of the coolant in the coolant channel closest to the streak. The temperature rise causes the coolant in that channel to expand, which lowers the density of the coolant and hence its cooling capacity, thereby compounding the hot streak and causing the temperature to rise even more, ultimately resulting in burnout of the channel and possibly total failure of the engine.
The limitations described above and others associated with rocket thrust engines that are cooled by multiple cooling channels are addressed by the present invention, which resides in a convergent-divergent rocket nozzle formed from two coaxially aligned conical sections that are joined at a throat plane with each section diverging outward from the plane, the wall of at least the upstream conical section containing coolant channels curving through the wall interior in spirals. The coolant flow paths established by these channels thereby traverse the axial direction of flow of the combustion gases inside the nozzle chamber. Any localized temperature excess (hot streak) in the gas stream in the combustion gas will therefore be cooled by a succession of coolant channels as the gas stream flows through the nozzle. Since heat exchange between the coolant and the hot streak will occur in only the small portion of each spiraling channel that traverses the hot streak, expansion of the coolant and reduction in coolant density is minimized.
The use of coaxially aligned conical sections as the convergent and divergent portions of the nozzle offers certain advantages in the design and construction of the nozzle. One of these advantages is the ability to form each portion of the nozzle from a single sheet or laminate of material and roll the sheet or laminate into a conical section by abutting the two opposing edges of the sheet or laminate along a single seam. The use of one seam rather than two or more reduces significantly the areas in which nozzle failure or cooling discontinuities can occur. The seam lowers the possibility of failure even more if the seam is spirally oriented rather than axial (i.e., longitudinal). When both the seam and the coolant channels are spirally oriented in the same direction, continuity of the coolant flow and ease of construction are both enhanced.
The closing of the sheet or laminate to form the conical section benefits further when the conical section consists of two or more nested conical section components each having been separately rolled into conical form prior to being combined with the other(s) in the nested arrangement. The nested components are arranged such that the seams of adjacent components are not superimposed. Thus, when the seams are spirally oriented, seams of adjacent component sections spiral either in opposite directions or in the same direction but out of phase. Once the individual components are stacked in the nested arrangement, the facing surfaces of the adjacent components are bonded together, thereby eliminating the need to bond the abutting edges of any single component section.
When nested conical component sections are used, each component can contain coolant channels that are independent of those of the adjacent component(s), thereby permitting the use of different coolant flow rates and heat transfer loads in each component. A higher coolant flow rate and heat transfer load is generally needed, for example, at locations immediately adjacent to the nozzle interior compared to locations closer to the nozzle exterior. The nested arrangement also facilitates the construction of complex coolant flow configurations such as coolant loops and transfers between the walls of the upstream and downstream conical sections.
Also disclosed herein is a novel method for joining the separately formed conical sections to form the convergent and divergent portions of the nozzle with a throat in between. According to this method, the convergent end of an individual conical section is split longitudinally into strips, the slits and strips beginning at the location where the throat will be formed. The strips are then spread outward at angles equal to the cone angle of the other conical section, and the two sections are combined by bonding the strips to the wall of the other conical section. Strips can be formed on both conical sections to join the sections even more strongly, the strips of the first conical section being bonded to the interior surface of the second conical section and the strips of the second conical section being bonded to the exterior surface of the first conical section, or vice versa.
The concept of splitting one end of a conical section into strips and the concept of using nested conical component sections can be applied jointly to a further advantage. Strips can be formed at the inlet end of the nozzle, i.e., the divergent end of the upstream conical section rather than the convergent end, the strips then turned first outward and then parallel to the nozzle axis to form the shell of an acoustic cavity. Nested components with similarly spaced strips are arranged with the strips of adjacent components overlapping, thereby closing the spaces between strips to form a continuous shell wall with no gaps.
Other features, advantages, and implementations of the concepts of this invention will be apparent from the description that follows.